Galaxies as Sources of Reionization

1. Galaxies as Sources of Reionization • Haojing Yan • (Carnegie Observatories) • Reionization Workshop at KIAA • July 10, 2008

2. Luminosity Function of Galaxies at z  6 — UV LF has a very steep faint-end slope Stellar Masses of Galaxies at z  6 — some high-mass, “old” galaxies already in place; but they are not likely the dominant reionzation sources. Implications for (HI) Reionization — dwarf galaxies did it! An Unanswered Question at z  6 — evolution ofLF at the bright-end? Outline

3. Part ILF of Galaxies at z  6 (5.5  z  6.5)

4. Source(s) of Reionization Yan & Windhorst 2004, ApJ, 600, L1 Critical value from Madau, Haardt & Rees 1999 Contribution from reionizing sources • Galaxies can account for the necessary reionizing photons, if the LF has a steep faint-end slope; dwarf galaxies are important contributors.

5. To z<30 mag, 108 i-dropouts found in the HUDF(Yan & Windhorst 2004, ApJ, 612, L93; YW04) Note: ~ 1.5 mag deeper than Bunker et al. (2004; MNRAS, 355, 374)

6. By pushing to the very limit of the HUDF, we start to be able to address the LF faint-end slope at z~6.

7. Detection Reliability at z>28.5 mag Level z’ i’ z’=29.23 z’=29.97

8. z=5.83; Dickinson et al. (2004) z=5.9; Malhotra et al. (2005)

9. GRAPES: i-dropouts success rate of ~ 90% in the HUDF to z~27.5 mag ACS Grism Observations of HUDF (GRAPES; Malhotra et al. 2005) z=6.0 z=6.4 z=6.1

10. Our HUDF z  6 candidate sample supports a very steep UV LF faint-end slope: α = -1.8 to -1.9 Dwarf galaxies can provide sufficient (re)ionizing photons at z  6 YW04 Constrain to the UV LF at z  6

11. Recent Result Confirms the Steep Faint-end Slope (Bouwens et al. 2006) 4.6x10-3 Msun/yr/Mpc3 1.1x10-2 Msun/yr/Mpc3 506 i-drops: UDF, UDF-Pars, GOODS “Lilly-Madau Diagram” But compare to YW04: M* = -21.03, * = 4.6x10-4/Mpc3 SFRis still uncertain by 2x

12. LAE : ~ 1/4 of the entire galaxy population (based on results at z~3), but still very important —easier to identify; current redshift record holder is the LAE at z=6.96 (Iye et al. 2006) LAE as probe of the reionization epoch : neutral IGM — Lya line suppressed—LAE number drop (e.g., Marilada-Escude 1998; Malhotra & Rhoads 2001) LAE at z  6 are usually selected at two narrow windows at z=5.7 & 6.5 in order to avoid strong night-sky lines Luminosity Function of z  6 LAE

13. Malhotra & Rhoads (2004): no evolution seen; IGM ionized up to z=6.5 Haiman & Cen (2005): not necessarily; local HII bubble permits escape of Lya photons and the suppression is not as large; <XHI> up to 25% Evolution of LAE LF from z=5.7 t0 6.5

14. Kashikawa et al. (2006): strong evolution from z=5.7 to z=6.5 ! Significant fraction of HI at z=6.5 ?? WMAP zreion ~ 11.4? Better Statistics from Subaru Deep Field Shimasaku et al. (2006) Kashikawa et al. (2006)

15. Part IIStellar Masses of Galaxies at z  6

16. Stellar mass density & SFR density:  =∫SFR dt Need measurements at rest-frame optical (and beyond) to reduce biases caused by dust extinction and short-lived stars when converting light to mass Study at high-z made possible by Spitzer IRAC GOODS Spitzer Legacy Program has played a critical role Stellar Mass Assembly History in Early Universe

17. IRAC Sees z ~ 6 Galaxies in HUDF z =5.83 galaxy 3.6μm 4.5μm 5.6μm 8.0μm

18. Three i-drops in HUDF securely detected by IRAC z=5.83 z=5.9 zp~5.9 Yan et al. 2005, ApJ, 634, 109

19. Some Major Conclusions from SED Fitting • Some high-mass (a few x 1010Msun) galaxies were already in place by z6 (age of Universe < 1.0 Gyr) • A few hundred Myr old (formed at z>>6) • Number density consistent with CDM simulation from Nagamine et al. (2004) See also Eyles et al. (2005)

20. Extending to Entire GOODS(Yan et al. 2006, ApJ, 651, 24) CDFS, 3.6μm HDFN, 3.6μm IRAC-detected i-dropouts

21. CDFS, 3.6μm HDFN, 3.6μm IRAC-invisible i-dropouts

22. Difficulty: no photometric info between z’ and IRAC 3.6μm • Have to take a different, simplified approach (z’-3.6μm) color  age for a given SFH  M/L for a given SFH at this age  stellar mass; repeat for all SFH in the set, and take min, max, median

23. Stellar Mass Estimates Summarized • IRAC-detected Sample • Mrep: 0.09 ~ 7.0x1010Msun (median 9.5x109Msun) • Trep: 50 ~ 400 Myr (median 290 Myr) • IRAC-invisible Sample, using 3.6m upper limit • Upper-limit of Mmax (median 4.9x109Msun)

24. Stacking of IRAC-invisible i-dropouts 3.6μm IRAC-invisible sample stack Random stack Mmin = 1.5x108 Mrep = 2.0x108 Msun Mmax = 5.9x109 3.6μm mag = 27.44 median z’ mag = 27.00

25. ΛCDM models seem to be capable of producing such high-mass galaxies by z  6 Implications (I): compare to simulation Models courtesy of K. Nagamine; based on simulations of Nagamine et al. (2004) and Night et al. (2006)

26. Lower limit at z ~ 6: (1.0, 1.6, 6.5) x 106MsunMpc-3 Implications (II): Global Stellar Mass Density

27. Implications (III): Source of Reionization • Critical SFRD based on Madau et al. (1999) • Progenitors of all IRAC-detected z6 galaxies formed simultaneously with the same e-SFH: SFR  e-t/ • The progenitors of high-mass galaxies alone CANNOT provide sufficient ionizing photons to sustain the reionization • Dwarf (low-mass, low-luminosity) galaxies, which could be more numerous, must have played an important role

28. Part IIIBright-end of LF at z  6

29. Bouwens et al. (2006): L*(z=6) = 0.6L*(z=3) Effect of large-scale structure ( “cosmic variance”)?? L* & Bright-end of LBG LF

30. Need Degree-sized Surveys to Minimize Impact of “Cosmic Variance” at Bright-end (Millennium Simulation slice at z=5.7)

31. Bright i-drops in 4-deg2 CFHTLS D1(2h-4d) (overlap SWIRE) D2 (10h+2d) (w/COSMOS) 16.5’x10’ GOODS- Size Area D4 D3 Yan et al. (in prep)

32. Magellan High-z LAE Survey Yan, McCarthy & Windhorst

33. Narrow-band imaging in 917nm & 971nm OH-free windows to search for LAE at z ≈ 6.5 & 7.0 Four IMACS f/2 fields (~ 0.9 deg2); reducing cosmic variance with limited telescope time Survey depth (5-) AB=25.0 mag (2.4510-17 erg/s/cm2 for pure-line sources; 7-810-18 erg/s/cm2 for continuum-detected sources) Aiming at bright-end of the luminosity function Survey Highlights

34. Survey Design: Filters ~ 400 Mpc3/arcmin2 6.46 — 6.62 6.91 — 7.07 o(917nm) p(971nm) (Before upgrading, SITe CCDs)

35. Use fields that have public, deep continuum images in multi-bands (especially in z’-band) Accessibility from Las Campanas CFHTLS Deep D1, D2 & D4 spreading out in RA Survey Design: Fields

36. 1-night in Feb. 2007 + 2-night in Mar. 2008, 1 IMACS pointing in COSMOS field (CFHTLS-D2), 20hr in o(917nm) 3-night in Jul. 2007, 1 IMACS pointing in CFHTLS-D4, 20 hr in o(917nm) Achieved desired depth Survey Status

37. COSMOS CFHTLS-D4 1o 1.48o 1o 1.48o

38. CFHTLSD4NW, 20hr in o 5- source counts

39. LAE Candidate Selection • Continuum images from the T0003 release of CFHTLS-D4 • z’-o>0.44 (flin/fcon>1.5) i’-z’>1.3 if detected in z’ non-detection in u’,g’ and r’ • For now only discussing candidates invisible in z’

40. 3 candidates invisible in continuum o=23.88 o=24.39 o=25.49? (Now seeking time do spectroscopic identification)

41. Rapid Evolution from z=5.7 to 6.6 or not? Kashikawa et al. 2006 (in Subaru Deep Field)

42. UV Luminosity Function of Galaxies at z  6 — a very steep faint-end slope (lots of dwarf galaxies …) Stellar Masses of Galaxies at z  6 — some high-mass, “old” galaxies in place; but not enough Implications for (HI) Reionization — dwarf galaxies did it! Unanswered questions at z  6: Bright-end of LF (LBG/LAE) should tell a lot — degree-sized surveys needed to reduce “cosmic variance” Summary